1. Field of the Invention
The invention relates to corrugated paper making machinery and more particularly to the lower corrugating rolls of such machinery.
2. Description of the Prior Art
For convenience in describing the prior art, prior art structures have been illustrated in FIGS. 1-5. A finger plate type construction is shown in FIG. 1 and a suction type construction is shown in FIG. 2. The single-facer shown in both of these figures comprises an upper corrugating roll 10 fluted on its outer peripheral surface and a similarly fluted lower corrugating roll 12. A web 14 fed from an earlier stage of the corrugated paper making machinery over the upper corrugating roll 10 is corrugated at the meshing portion between the upper roll 10 and the lower roll 12.
After the web 14 has been corrugated at the meshing portions, paste is applied to the flute crests of the corrugated web, identified by the numeral 16, from a pasting roll 18. The corrugated web 16 is then bonded to a liner web 20, fed over a pressure roll 22, to form the single-faced corrugated board 24. The bonding is effected by pressure exerted between the pressure roll 22 and the lower corrugating roll 12, and the single-faced corrugated board 24 is then fed to a subsequent stage of the machinery.
In the finger plate type construction shown in FIG. 1, finger plates 26 are provided along the outer peripheral surface of the lower corrugating roll 12 to counteract a tendency of the corrugated web 16 to move away from the lower corrugating roll 12, as illustrated in FIG. 3, under the influence of centrifugal force and to counteract the tendency of internal stress generated in the corrugated web 16 to restore the paper to its original flat form. In the suction type construction shown in FIG. 2 a plurality of passages 27 are provided in the lower corrugating roll 12' extending between the hollow interior portion 28 of this roll and the exterior peripheral surface thereof. A suction force is applied through the interior portion 28 to the corrugated web 16 passing over the exterior of the roll 12' to maintain the corrugated web in engagement with the flutes of the roll and to counteract the aforementioned tendencies.
The finger plate construction shown in FIG. 1 has the disadvantage that it is necessary to provide a substantial number of such finger plates 26 at spaced intervals along the length of the roll in order to accomplish the aforementioned purposes. Paste cannot be applied to the crests of the corrugated web 16 at the points where these finger plates are disposed and as a result the mechanical strength of the formed corrugated board is reduced below that which could otherwise be achieved. Further, the finger plates 26 have a relatively short life and usually have to be replaced in less than one month. Moreover, adjustment of the gap clearance between the finger plates 26 and the lower corrugating roll 12 is very critical; if the clearance is too great the precision in corrugation is degraded, whereas if it is too small there is a risk of damaging the corrugated web 16.
This shortcoming of the finger plate type construction is not present in the suction type construction shown in FIG. 2. As shown in more detail in FIGS. 4 and 5 this type of structure includes a plurality of circumferential grooves 30 on the outer peripheral surface of the roll 12'. These grooves are connected with the hollow interior portion 28 of the roll through the plurality of passages 27 providing communication between the grooves 30 and the interior portion 28. Suction is applied through a passage 34 at one end of the hollow interior porton 28, and the resulting negative pressure is applied to the corrugated web 16 through the passages 27 and the grooves 30 to cause the corrugated web to be held against the exterior fluted surface of the corrugated roll 12'.
However, a roll of this type requires a great deal of machining time and expense because several hundred holes or passages 27 are required and the diameter of these passages is necessarily small because the width of the grooves is narrow. Further, the roll has a very high hardness and the wall thickness is substantial. Another problem is that these holes, each being of small diameter and including a long straight portion, are susceptible to being blocked frequently by dust, dregs of paste, paper powder, etc. When some of the passages become blocked in this manner the corrugated web is not held properly against the roll and there is a degradation of quality. To keep the holes clear and avoid this degradation of quality requires substantial maintenance.
In the effective bonding of the elements of corrugated paper board a large amount of heat is necessitated and normally this heat is conveniently applied by introducing steam to the interiors of the hollow rolls. However, in the type of construction shown in the illustrated prior art steam cannot be introduced into the lower corrugating roll because of the necessity to utilize a vacuum therein. To overcome this problem preheating rolls were provided before the upper corrugating roll 10 and the pressure roll 22 to supply the required heat. However, such heating is inefficient and not suitable for high speed operations. Moreover, since the lower corrugating roll is not heated and since it receives radiant heat from the upper corrugating roll 10 and the pressure roll 22, the lower corrugating roll may become deformed and thus reduce product quality. Further, since the temperature of the lower corrugating roll is low, and the passages 27 are of small diameter and substantial length, there is a greater risk of blocking the passages 27 by paste sputtered from the pasting roll onto the lower corrugating roll where the paper web is not present, increasing the required maintenance.
Another prior art structure, not illustrated, does provide an arrangement where both heat and vacuum may be supplied through the hollow interior of the lower corrugating roll but this structure results in greater complexity of construction. Moreover, it does not provide as effective a force as the structure of the present invention in retaining the corrugated web in engagement with the lower corrugating roll for an appropriate interval and it does not include the provision of the present invention for insuring effective separation of the corrugated web from the corrugating roll at the appropriate time.
By the present invention these deficiencies of the prior art structures are overcome and a lower corrugating roll is provided in which machining is relatively easy, the blocking of the suction holes is eliminated, maintenance is reduced and better quality of corrugated paper board is insured. Further, the present invention provides both heat and suction in a relatively simple construction. Finally, it provides ejection means for promptly removing any paste or other materials which may find their way into the passages, thereby insuring continuous effectiveness of these passages.